The invention relates to a switching coupling (1a) for a connectable or disconnectable viscous coupling (1b), which serves to distribute the driving torque between the driving axles and/or wheels of a motor vehicle, and includes a hollow shaft (17), a shaft journal (19) coaxially supported therein, radially movable locking elements (24) which are held in guiding apertures (22) of the hollow shaft (17) so as to be circumferentially fixed, but radially movable, which cooperate with corresponding engaging recesses (23) in the shaft journal which are axially associated with the guiding apertures (22) in the hollow shaft (17) and which may be engaged by the locking elements (24) for non-rotatingly connecting the hollow shaft (17) to the shaft journal (19), as well as having a locking ring (24) which, to a limited extent, is axially movable on the hollow shaft (17) and which comprises a contact face for radially displacing the locking elements (24) inwardly and a blocking face for holding the locking elements (24) while simultaneously engaging the hollow shaft (17) and shaft journal (19).
Disconnectable couplings, especially viscous couplings, are used in the driveline of four wheel drive vehicles to have the option of engaging the second axle when special operating conditions prevail, for instance, in the case of bad traction or slip at the permanently driven axle or for disconnecting the second axle under certain operating conditions to ensure driving stability and error-free functioning of an anti-blocking system.
A coupling of this type is known from DE 38 22 115 A1, in which the force-transmitting mechanism consists of a claw coupling, with the axially displaceable claw sleeve being locked via spherical locking elements which engage a groove in the respective hollow shaft and which, via a locking sleeve, are held radially against the tooth force of the claw coupling. These couplings are hardly suitable for connecting and disconnecting purposes under load.
From DE 37 07 115 A1, it is known to preload a limited slip differential axle with a variable friction resistance via an electromagnetic control device, thus providing the driver with a pre-setting for different road conditions. Because of the existing friction damage, this assembly is subject to increased wear, and its control device does not permit the short switching times such as are required for a four wheel drive vehicle with an anti-blocking system.